A tooth of a digging bucket of an excavator is a working member which is subjected to an intensive abrasive wear during operation and to heavy impact and static loads which determine its service life. A tooth of an excavator bucket performs two main functions: it plunges into rock, it breaks-up the rock and guides the broken particles of rock into the excavator bucket. The construction of the excavator bucket tooth determines the character and magnitude of impact loads influencing reliablility of all assemblies and mechanisms of the excavator which, in the end of the day, determine productivity of the excavator. It should be also noted that replacement of worn or deformed teeth is a very tedious and time-consuming process. For example, it takes up to eight hours to replace a set of teeth of an excavator bucket having six-seven teeth, with the weight being each tooth of about 500 kg. Therefore, the problem of prolonging service life of teeth of an excavator digging bucket is a very important problem.
When a tooth of an excavator digging bucket plunges into the rock, a flow of particulate rock moves along its top surface, the flow of particulate rock at the starting portion of the tooth of a comparatively short length being of laminar nature. The flow of particulate rock then leaves the tooth surface which results in a material increase, from twenty to forty times, in resistance to penetration of the tooth in the rock. To lower this resistance, the portion of the tooth surface adjacent to the portion where the laminar flow of particulate rock leaves the tooth is made concave. The flow of particulate rock at this portion changes from laminar to turbulent so as to determine a positive formation of vortices in the boundary layer of particulate rock which is adjacent to the top surface of the tooth at the concave portions. The major part of coarser particulate rock moves over the vertices of the boundary layer. Therefore, intensity of abrasive wear of the tooth is determined by the character of movement of particulate rock in the boundary layer.
Known in the art is a tooth for a digging bucket of an excavator (U.S. Pat. No. 3,959,901) having a wedge-like profile defined by two surfaces extending at an angle with respect to each other. The top surface has two portions of an undulated configuration which are separated by a ridge.
The end of the tooth is pointed or has a comparatively small radius of curvature. The undulated shape of the top surface of the tooth lowers intensity of abrasive wear of the top surface of the tooth. However, the pointed end of the tooth plunges into the rock to break it with the formation of a large amount of dust particles and very fine particles of a size between 26 and 50 mm. Owing to a large amount of dust and fine particles of particulate rock which are in contact with the top surface of the tooth the intensity of its abrasive wear is rather high so as to substantially shorten service life of the tooth. It should also be noted that rock is broken down with substantial impact loads which also shorten service life of teeth of an excavator bucket.
Known in the art are teeth for excavator digging buckets having a groove in the end face widthwise of the tooth, which lowers impact loads acting upon the tooth when it breaks down the rock. The groove concentrates break down energy at a distance of about 0.237 m from the end face of the tooth in the rock body, and a dense core of dust particles is formed directly in front of the end face of the tooth which lowers impact loads owing to the deformation of this core and which initiates separation of a block of rock of about 0.237 m from the rock body.
It is known from the grading data that between 20 and 25% of the broken rock volume are in the form of particles of a size between 0.025 and 0.035 m and the content of dust particles is beteen 2 and 4%, the rest being coarser particles of 0.08 m and larger.
Known in the art is a tooth for a digging bucket of an excavator (U.S. Pat. No. 1,146,442) having a wedge-like profile defined by two surfaces extending at an angle with respect to each other, at least one surface being of an undulated configuration with at least two convex portions conjugated by a concave portion, the two surfaces being conjugated by an end face having a groove extending widthwise of the tooth. The top and back surfaces of the tooth are undulated. The profile of the undulated surfaces of the tooth is close to a sinusoid, and movement of the boundary layer formed by dust particles along the surface of the concave portions, on which movement of the boundary layer is turbulent, occurs with a slip so that the top surface of the tooth is subjected to an intensive abrasive wear. In addition, during slippage of the boundary layer on the pressure surges occur on the back surface so as to result in an increase in its wear.